There is known active gate control (AGC) which actively controls a gate voltage or a gate current as a technique for eliminating a trade-off between a surge voltage and a switching loss during a switching operation in a power switching element that constitutes a semiconductor power conversion device such as an Inverter or a converter.
For example, when an insulated gate bipolar transistor (IGBT) is used as a power switching element, a change with time dV/dt of a collector-emitter voltage (hereinbelow, referred to as a collector voltage Vce) during turning-off is fed back to control a discharging speed of a gate charge of the IGBT. Specifically, Patent Literature 1 proposes a technique for switching the discharging speed of the gate charge of the IGBT in the middle of discharge.
As the switching timing, for example, when the switching is performed at the timing when the collector voltage Vce reaches a power supply voltage VB, it is possible to reduce the switching loss while reducing surges.
However, dV/dt in a power switching element such as an IGBT typically has a temperature dependence. Thus, the switching timing of the discharging speed of the gate charge in the power switching element changes by the temperature of the power switching element.
For example, Patent Literature 2 proposes a technique for adjusting a feedback amount of dV/dt according to the temperature of the power switching element as a drive circuit that takes into consideration the temperature characteristics of the power switching element. Specifically, a feedback resistance (base-GND resistance) of a transistor for turning-off is made variable according to the temperature. Accordingly, it is possible to control the discharging speed of the gate charge according to the temperature.
However, the technique of Patent Literature 2 defines the discharging speed of the gate charge, that is, defines the drive capacity according to the temperature of the power switching element, and cannot eliminate the trade-off between the surge voltage and the switching loss. Further, even when the technique described in Patent Literature 2 and the technique described in Patent Literature 1 are combined, it is difficult to optimize the switching timing of the discharging speed. Thus, an effect of reducing the switching loss is not sufficient.